1. Field of the Invention
The present invention is directed to a transmission/reception arrangement for a diagnostic magnetic resonance apparatus of the type having an antenna, a matching and tuning circuit, and a signal transmission line, the antenna being fashioned together with the matching and tuning circuit for exciting and/or receiving proton magnetic resonance signals at a particular frequency.
2. Description of the Prior Art
U.S. Pat. No. 4,467,282 discloses a transmission/reception arrangement of the above type. The apparatus has an antenna for exciting and/or receiving proton magnetic resonance signals at a frequency that is determined by the basic magnetic field. The relationship between the frequency of the magnetic resonance signals and the basic magnetic field is predetermined by the gyromagnetic constant. To compensate for detuning of the antenna as a result of the introduction of a patient to be examined into the examination volume, a matching and tuning two-port circuit is provided. The matching and tuning circuit is fundamentally composed of an adjustable series capacitance and an adjustable parallel capacitance as disclosed in detail in, for example, U.S. Pat. No. 5,208,537. The antenna is optimized for proton imaging for employment in medical diagnostics.
Multiply resonant antenna arrangements as disclosed, for example, in U.S. Pat. No. 4,742,304, are employed for magnetic resonance spectroscopy examination. The matching and tuning circuit belonging to the antenna is fashioned so as to be multiply resonant therein.
Imaging with hyperpolarized gases a topic currently under active discussion in this field, for example, for imaging the lung, which offers new employment possibilities for a whole-body magnetic resonance apparatus. Imaging with inert gases such as, for example, xenon (.sup.129 Xe) and helium (.sup.3 He) that are polarized by optical pumping with a laser light source are in the foreground of the discussions involving this technique. Polarization degrees of above 50% thus can be achieved. The gyromagnetic constants of .sup.129 Xe and .sup.3 He, however, differ substantially from the gyromagnetic constant of hydrogen. Whereas hydrogen has a gyromagnetic constant of 42.7 MHZ per Tesla, the gyromagnetic constant of .sup.3 He is only approximately 32.3 MHZ per Tesla and that of .sup.129 Xe is only approximately 11.8 MHZ per Tesla. Some non-hyperpolarized gases also exhibit imaging properties that can be utilized in medical diagnostics. These Include gases that contain fluorine such as, for example, carbon tetrafloride (CF.sub.4) and sulfurhexafluoride (SF.sub.6). As in conventional proton imaging, these gases are polarized with a highly uniform basic magnetic field. The gyromagnetic constant of fluorine, at 40 MHZ per Tesla differs significantly from the gyromagnetic constant of protons. A conventional resonance apparatus thus can not be employed without further modification for imaging of hyperpolarized gases or such non-hyperpolarized gases. In particular, the employment of a conventional whole-body transmission antenna for lung imagings making use of the imaging processes of these gases would be desirable because of the large-volume and uniform excitation which could be achieved.